Step variable transmission for a motor vehicle

ABSTRACT

A step variable transmission for a motor vehicle has a plurality of forward gear stages and at least one reverse gear stage. The transmission comprising: a drive input shaft arrangement, a drive output shaft arrangement, and a plurality of wheel sets which have loose wheels and shift wheels, wherein the shift wheels are rotatably mounted on a shaft arrangement and can be rotationally fixedly connected to the associated shaft arrangement by means of respective shift clutches.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of application Ser. No. 11/750,956filed May 18, 2007 which is a Continuation application of theInternational patent application PCT/EP2005/012098, filed Nov. 11, 2005,claiming the priority of German patent application DE 10 2004 056 936,filed Nov. 23, 2004, the entireties of which are incorporated byreference herein.

BACKGROUND OF THE INVENTION

The present invention relates to a step variable transmission for amotor vehicle, wherein the step variable transmission has a plurality offorward gear stages and at least one reverse gear stage.

The present invention more precisely relates to an automatic stepvariable transmission in which the engagement and disengagement of gearstages is carried out by means of actuators. Selector drums, which aredriven electromotively, hydraulic linear actuators, etc. can be used asactuators.

The present invention relates in particular to twin-clutch transmissionsand automatic shift transmissions.

Twin-clutch transmissions are for example known from the documents DE198 21 164 A1, EP 0 083 747 A2, EP 0 046 373 A1.

Automatic shift transmissions are provided in the Smart®, in the BMW® M3and in the recently introduced BMW® M5. The latter involves a 7-gearautomatic shift transmission. Said automatic shift transmission has awheel set arrangement which does not follow the conventional H-pattern.In particular, shift clutch packs which have two shift clutches areassigned to not directly successive gears. Since the shift clutch packshave separate actuators in each case, the disengagement of a source gearand the engagement of a target gear can take place with a certain timeoverlap, so that gear changes can be carried out very quickly.

In twin-clutch transmissions, the forward gears are divided between twopartial transmissions. Here, it is generally the case that odd gears areassigned to one partial transmission and even gears are assigned to theother partial transmission. Each partial transmission is connected bymeans of a separate clutch to the drive output shaft of the drive motor.With a twin-clutch transmission, gear changes can be carried out withoutan interruption in tractive force by means of overlapping actuation ofthe two clutches.

The two transmissions types (twin-clutch transmission and automaticshift transmission) however still do have room for improvement.

BRIEF SUMMARY OF THE INVENTION

It is accordingly the object of the present invention to specify animproved step variable transmission for a motor vehicle.

Said object is achieved by means of a step variable transmission for amotor vehicle, wherein the step variable transmission has a plurality offorward gear stages and at least one reverse gear stage, having a driveinput shaft arrangement, an output shaft arrangement, and a plurality ofwheel sets which have loose wheels and shift wheels, wherein the loosewheels are rotatably mounted on a shaft arrangement and can berotationally fixedly connected to the associated shaft arrangement bymeans of respective shift clutches.

The step variable transmission is preferably a twin-clutch transmission,wherein the drive input shaft arrangement has a first and a second driveinput shaft which are assigned to a first and a second partialtransmission respectively, and wherein the first partial transmission isassigned odd forward gear stages and the second partial transmission isassigned even gear stages.

In the twin-clutch transmission of said type, it is particularlypreferable if the forward gear stage which is used predominantly forstarting the motor vehicle in the forward direction and the reverse gearstage are assigned to different partial transmissions.

The forward gear stage which is used predominantly for starting themotor vehicle is generally the first gear. As a result of the assignmentto in each case a different partial transmission, it is not necessary toshift between the gear stages in the event of changes in the travelingdirection. In other words, were the starting gear stage and the reversegear stage assigned to the same partial transmission, it would benecessary in the event of a change in the traveling direction to alwaysinitially disengage the one gear stage and engage the other gear stage.This leads to undesirably long gear change times in particular in the socalled free-rocking mode in the event of a vehicle becoming stuck.

According to the preferred embodiment, in contrast, no shift orsynchronizing processes which would load the shift clutches(synchronizations) are necessary. Starting processes in the forwarddirection and in the reverse direction are also generally carried outwith different transmission-input-side starting clutches. Accordingly,the two starting clutches of the twin-clutch transmission are loadedmore uniformly.

When starting the motor vehicle, the reverse gear stage and the startingforward gear stage are preferably engaged at the same time. Thisimproves the capability of the transmission for cold shifting since, forstarting in any direction, no engagement process need be carried outwhile the transmission is at rest.

According to a further preferred embodiment, the drive input shaftarrangement has a single drive input shaft.

In said embodiment, the step variable transmission is for example anautomatic shift transmission.

It is advantageous overall if the drive output shaft arrangement has twodrive output shafts which, together with the drive input shaftarrangement, form a 3-shaft arrangement.

Step variable transmissions of said type can be of particularly compactdesign in the axial direction.

Here, in a twin-clutch transmission, the forward gear stages of apartial transmission can be distributed between the two drive outputshafts.

The “assignment” of a gear stage to a drive output shaft means that theshift clutch which serves to engage and disengage said gear stage ismounted on said driveshaft.

Here, it is particularly advantageous if a certain forward gear stage isassigned to one drive output shaft of the output drive shafts and if thereverse gear stage is assigned to the other drive output shaft.

It is particularly advantageous here if the reverse gear stage is drivenvia the certain forward gear stage.

In said embodiment, the fact that two drive output shafts are providedis utilized to realize the rotational direction reversal required forthe reverse gear. In other words, in said embodiment, no furtherauxiliary shaft is required for mounting a rotational direction reversalwheel. The rotational direction reversal takes place here in that therotational direction is initially reversed by means of the certainforward gear stage.

It is particularly advantageous here if the reverse gear stage is drivendirectly via the certain forward gear stage.

In said embodiment, no further gearwheel is required for rotationaldirection reversal.

In an alternative embodiment, the reverse gear stage is driven via awheel which is rotationally fixedly connected to a loose wheel of awheel set which is assigned to the certain forward gear stage.

In said embodiment, the loose wheel of the certain forward gear stage istherefore rotationally fixedly connected to the further wheel. As aresult of said measure, the transmission ratio for the reverse gearstage can be freely selected in wide ranges.

It is also advantageous if a parking lock is assigned to one of thedrive output shafts.

This firstly has the advantage that the accommodation of the parkinglock requires only a small amount of installation space. In particular,no separate parking lock shaft is required. The arrangement of theparking lock on a differential gearing which is connected downstreamwould be also generally more structurally complex, requires more add-onparts and increases costs. In addition, a parking lock on thedifferential gearing would require a more massive design, since thetorques introduced there by the drive output are higher than on one ofthe drive output shafts.

In other words, the torques or forces acting on the parking lock arereduced, specifically corresponding to a drive output constanttransmission ratio.

It is to be noted in this regard that the two drive output shafts of theembodiment according to the invention are generally connected to adifferential gearing by means of a respective drive output constantwheel set.

By arranging the parking lock on one of the provided drive outputshafts, the parking lock can be of smaller and more cost-effectivedesign overall.

It is also particularly advantageous if the parking lock is aligned inthe axial direction with a certain forward gear stage of the other driveoutput shaft.

Further installation space can be saved in this way.

It is particularly advantageous if the reverse gear stage is driven viaa wheel which is rotationally fixedly connected to a loose wheel of awheel set which is assigned to the certain forward gear stage. In thiscase, the additional axial length, on the one drive output shaft, forthe further wheel on the other drive output shaft is so to speak “filledup” by the parking lock.

It is particularly advantageous overall if the certain forward gearstage is the second forward gear stage.

Since the reverse gear stage and the forward gear stage used forstarting in the forward direction (generally the first gear) arepreferably assigned to different partial transmissions, it is then notpossible to drive the reverse gear stage by means of the first gear.

The second forward gear stage (the second gear) is therefore used forthis purpose. It is hereby possible to still provide a sufficientlyfavorable transmission ratio for starting in reverse gear. It ispossible in particular to realize a transmission ratio for the reversegear which is close to that of the first gear.

According to a further preferred embodiment, in the twin-clutchtransmission, two forward gear stages of the forward gear stages of onepartial transmission are assigned to different drive output shafts,wherein said two forward gear stages share a common fixed wheel on thedrive input shaft arrangement.

In said embodiment, a so-called “dual use” of the fixed wheel isrealized. This brings about weight savings, installation space savingsand cost savings. It is self-evident that the two working gear stageswhich are related by means of a common fixed wheel must have a certaintransmission ratio relationship.

Although the realization of a single dual use generally entails the bestcomprise between functionality, costs and installation space, it ispossible for in each case two forward gear stages of the forward gearstages of the two partial transmissions to be assigned to differentdrive output shafts, wherein the respective two forward gear stagesshare in each case one common fixed wheel on the drive input shaftarrangement.

Two dual uses are therefore realized in said embodiment.

It is of course generally also conceivable to realize more than two dualuses.

According to a further preferred embodiment, the first forward gearstage (the first gear) and the second forward gear stage (the secondgear) are assigned to one of the two drive output shafts.

In this way, the transfer of high torques from the first gear to thesecond gear and vice versa takes place without a change of drive outputshaft. This has a positive effect on the noise and vibration generationof the transmission. There is no additional cost and installation spaceexpenditure and no restriction to the functionality of the transmission.

It is also advantageous if the first forward gear stage is assigned tothe drive output shaft with the shorter axle spacing.

This results in a small shift wheel diameter, which has a positiveeffect on the radial installation space for the axle shafts.

According to a further alternative embodiment, the drive output shaftarrangement has a single drive output shaft.

This provides a “classic” 2-shaft concept of a lay shaft reductiongearing design.

In said embodiment, the transmission has a greater overall axial lengthbut is generally of more compact design in the radial direction.

It is advantageous overall if those wheel sets which are assigned to theforward gear stages which transmit high torques are arranged at the endsof the drive input shaft arrangement.

In other words, gears with a large shift wheel diameter are preferablysituated at the drive output shaft ends. Gear stages with small shiftwheel diameters are preferably arranged in between. This leads, inaddition to the positive effect on the shaft bending, to so-called“package” advantages. The (hydraulic, pneumatic, electromechanical,etc.) shift actuating arrangement, preferably a selector drum actuatingarrangement, can then be arranged, radially close to the drive outputshafts, between the gears with large shift wheel diameters.

The step variable transmission can be embodied as a transmission withfive or six forward gear stages or else as a transmission having morethan six forward gear stages, for example as a 7-gear transmission. Theabove-stated advantages have a particularly pronounced effect in thecase of a 6-gear transmission.

The beveling direction of the fixed wheels is preferably designed suchthat the reaction forces from the torque loading under traction act inthe same direction as the clutch actuating forces, which are higher thansaid reaction forces. No axial movement of the drive input shaftstherefore takes place in the event of transitions from traction tooverrun, which has a positive effect on the controllability of theclutches.

It is possible overall according to the invention to provide compact,cost-effective, functionally high-quality and robust step variabletransmissions.

It is self-evident that the features specified above and the featuresyet to be explained below can be used not only in the respectivelyspecified combination but also in other combinations or individuallywithout departing from the scope of the present invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

Exemplary embodiments of the invention are illustrated in the drawingand are explained in more detail in the following description. In thedrawing:

FIG. 1 shows a schematic wheel set diagram of a first embodiment of atwin-clutch transmission according to the invention;

FIG. 2 shows a schematic cross-sectional view of the twin-clutchtransmission of FIG. 1;

FIG. 3 shows a schematic wheel set diagram of a second embodiment of adifferential gearing according to the invention;

FIG. 4 shows a schematic wheel set diagram of a third embodiment of adifferential gearing according to the invention;

FIG. 5 shows a schematic wheel set diagram of a fourth embodiment of atwin-clutch transmission according to the invention;

FIG. 6 shows a schematic wheel set diagram of a fifth embodiment of atwin-clutch transmission according to the invention;

FIG. 7 shows a schematic wheel set diagram of a sixth embodiment of atwin-clutch transmission according to the invention;

FIG. 8 shows a schematic wheel set diagram of a seventh embodiment of atwin-clutch transmission according to the invention;

FIG. 9 shows a schematic wheel set diagram of a first embodiment of anautomatic shift transmission according to the invention; and

FIG. 10 shows a schematic wheel set diagram of an eighth embodiment of atwin-clutch transmission according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, a first embodiment of a twin-clutch transmission according tothe invention is denoted generally by 10.

The twin-clutch transmission 10 has a first drive input shaft 12 and asecond drive input shaft 14. The second drive input shaft 14 is embodiedas a hollow shaft and is arranged concentrically with respect to thefirst drive input shaft 12.

The first drive input shaft 12 can be connected to a first clutch K1.The second drive input shaft 14 can be connected to a second clutch K2.

The first drive input shaft 12 extends over a greater axial extent thanthe second drive input shaft and projects beyond the latter.

The twin-clutch transmission 10 also has a first output shaft 16 and asecond output shaft 18. The two output shafts 16, 18 are arranged ineach case parallel to the drive input shafts 12, 14 and are connected,by means of a output constant wheel set, to a differential drive inputwheel 24 of a differential gearing 26.

More precisely, the output constant wheel set has a first output wheel20 which is rotationally fixedly connected to the first output shaft 16,and has a second output wheel 22 which is rotationally fixedly connectedto the second output shaft 18.

The two output wheels 20, 22 are aligned with one another axially andboth engage with the differential drive input wheel 24, as can be seenin particular in FIG. 2.

The twin-clutch transmission 10 has six forward gear stages 1-6 and onereverse gear R. The odd forward gear stages 1, 3, 5 are assigned to afirst partial transmission of the twin-clutch transmission 10 andtherefore to the first clutch K1.

The even forward gear stages 2, 4, 6 and the reverse gear stage R areassigned to a second partial transmission of the twin-clutchtransmission 10 and therefore to the second clutch K2.

The forward gear stages 1, 2 and 6 are assigned to the first driveoutput shaft 16. The forward gear stages 3, 4 and 5 and the reverse gearstage R are assigned to the second drive output shaft 18.

A shift clutch pack SK1 having one shift clutch is mounted on the firstdrive output shaft 16 and is assigned to the forward gear stage 1. Ashift clutch pack SK2/6 having two shift clutches is assigned to theforward gears 2, 6. Correspondingly, a shift clutch pack SK3/5 havingtwo shift clutches is assigned to the forward gear stages 3, 5 and ashift clutch pack SK4/R is assigned to the gear stages 4, R.

The shift clutches provided in the shift clutch packs SK are for exampleembodied as conventional synchronous clutches.

Arranged on the first output shaft 16, in this sequence proceeding fromthe transmission input, are: the first output wheel 20, the loose wheelfor the forward gear stage 2, a rotational direction reversal wheel 28for the reverse gear stage R, the shift clutch pack SK2/6, the loosewheel for the forward gear stage 6, the shift clutch pack SK1, and theloose wheel for the forward gear stage 1.

Correspondingly arranged on the second output shaft 18, in this sequenceproceeding from the transmission input, are: the second output wheel 22,a parking lock 30, the loose wheel of the reverse gear stage R, theshift clutch pack SK4/R, the loose wheel for the forward gear stage 4,the loose wheel for the forward gear stage 5, the shift clutch packSK3/5, and the loose wheel for the forward gear stage 3.

The rotational direction reversal wheel 28 and the loose wheel for theforward gear stage 2 are rotationally fixedly connected to one another.The rotational direction reversal wheel 28 is aligned axially with theloose wheel of the reverse gear stage R on the second output shaft 18.Correspondingly, the parking lock 30 is aligned axially with the loosewheel for the second forward gear stage 2 on the first drive outputshaft 16.

In addition, the forward gear stages 4, 6 are aligned axially with oneanother and mesh with a common shift wheel 32. In other words, a dualuse of the forward gear stages 4, 6 is realized.

In the transmission 10, the forward gear stage 1 and the reverse gearstage R are situated on different partial transmissions and aretherefore assigned to different clutches K1 and K2.

The reverse gear stage R is driven via the rotational direction reversalwheel 28 of the forward gear stage 2, that is to say so to speak bymeans of the stepped second gear. Here, it is possible to realize atransmission ratio similar to that of the first gear.

The parking lock 30 is attached opposite the loose wheel or shift wheelof the forward gear stage 2.

One dual use is realized. The forward gear stages 1, 2 are situated onone output shaft, the output drive shaft 16. In total, four synchronousclutch packs SK are provided.

The forward gear stage 1 is situated on the output shaft 16 with theshort axial spacing. The gear stages with a large shift or loose wheeldiameter (in the present case, the gear stages 1 and 2 on the outputshaft 16 and the gear stages 3 and R on the output shaft 18) arearranged axially at the outside, so that an actuating arrangement can bearranged in between, radially close to the output shafts 16, 18.

The twin-clutch transmission 10 is embodied as an automatictransmission. The shift clutch packs SK are connected to correspondingactuators. Correspondingly, the clutches K1 and K2 are also actuatedautomatically.

As shown in FIG. 2, the output shaft 16 has a shorter axial spacing S1to the drive input shaft 12 than the axial spacing S2 of the secondoutput shaft 18 to the drive input shaft 12.

Further embodiments of step variable transmissions according to theinvention are described below. The embodiments of step variabletransmissions according to the invention explained below are generallyof a similar design to the transmission 10 of FIGS. 1 and 2. Thefollowing text therefore explains merely differences with respect to theembodiment of FIGS. 1 and 2. The description of the twin-clutchtransmission 10 otherwise also relates to the embodiments explainedbelow. Identical elements are therefore also provided with the samereference symbols.

FIG. 3 shows a second embodiment of a twin-clutch transmission 10 aaccording to the invention.

In the embodiment of FIG. 3, the wheel sets of the forward gear stages 4and 6 are not aligned axially with one another, and therefore no dualuse is realized. This has the advantage that no restrictions in thetransmission ratios are necessary. Furthermore, the transmission ratiosare modularly variable, for example for variants of gasoline/dieselengines. There is a slight increase in length over the twin-clutchtransmission 10 of FIG. 1.

FIG. 4 shows a further embodiment of a twin-clutch transmission 10 baccording to the invention.

In the twin-clutch transmission 10 b, in contrast to the twin-clutchtransmission 10 of FIG. 1, two dual uses are realized. More precisely,the forward gear stages 4, 6 and the forward gear stages 3, 5 arealigned axially with one another. The loose or shift wheels of theforward gear stages 3 and 5 thereby share a fixed wheel 34 on the firstdrive input shaft 12.

The axial sequence of the individual elements on the drive output shafts16 and 18 has also changed here. Arranged on the first output shaft 16,in this sequence proceeding from the transmission input, are thefollowing elements: the first output wheel 20, the loose wheel for thesecond forward gear stage, the rotational direction reversal wheel 28,the shift clutch pack SK2/6, the loose wheel of the forward gear stage6, the loose wheel of the forward gear stage 5, the shift clutch packSK1/5, and the loose wheel of the forward gear stage 1.

Correspondingly arranged on the second output shaft, in this sequenceproceeding from the transmission input, are the following elements: thesecond output wheel 22, the parking lock 30, the loose wheel of thereverse gear stage R, the shift clutch pack SK4/R, the loose wheel ofthe forward gear stage 4, the loose wheel of the forward gear stage 3,and the shift clutch pack SK3 for the third forward gear stage.

FIG. 5 shows another embodiment of a twin-clutch transmission 10 caccording to the invention.

The twin-clutch transmission 10 c has, in contrast to the twin-clutchtransmission 10 of FIG. 1, only five forward gears. This is advantageousin particular in low-cost vehicles which do not require six gears. Nodual uses are realized, and therefore there are no restrictions withregard to the transmission ratios.

The sequence of the elements on the first output shaft 16 is thefollowing: the first output wheel 20, the loose wheel for the forwardgear stage 2, the rotational direction reversal wheel 28, the shiftclutch pack SK2, the shift clutch pack SK1, and the loose wheel for theforward gear stage 1.

Arranged on the second output shaft 18 are the following elements: thesecond output wheel 22, the parking lock 30, the loose wheel of thereverse gear stage R, the shift clutch pack SK4/R, the loose wheel forthe forward gear stage 4, the loose wheel for the forward gear stage 5,the shift clutch pack SK3/5, and the loose wheel for the forward gearstage 3.

FIG. 6 shows a further embodiment of a twin-clutch transmission 10 daccording to the invention.

The twin-clutch transmission 10 d is again a low-cost variant for motorvehicles which do not require six gears. A short overall axialinstallation length is achieved, since a dual use is realized,specifically for the forward gear stages 3, 5.

The sequence of the elements on the first output shaft 16 is thefollowing: the first output wheel 20, the loose wheel for the forwardgear stage 2, the rotational direction reversal wheel 28, the shiftclutch pack SK2, the loose wheel for the forward gear stage 5, the shiftclutch pack SK1/5, and the loose wheel for the forward gear stage 1.

Arranged on the second output shaft 18 are: the second output wheel 22,the parking lock 30, the loose wheel for the reverse gear stage R, theshift clutch pack SK4/R, the loose wheel for the forward gear stage 4,the loose wheel for the forward gear stage 3, and the shift clutch packSK3.

FIG. 7 shows a further embodiment of a twin-clutch transmission 10 eaccording to the invention.

This is also a low-cost variant for motor vehicles which do not requiresix gears. The number of components is again reduced to a minimum. Onlythree shift clutch packs SK are required. Furthermore, the twin-clutchtransmission 10 e is particularly short in the axial direction, since adual use is realized (for gear stages 3, 5).

Arranged on the first output shaft 16 are: the first output wheel 20,the loose wheel for the forward gear stage 2, the rotational directionreversal wheel 28, the shift clutch pack SK2/5, and the loose wheel forthe forward gear stage 5.

Arranged on the second output shaft 18 are: the second output wheel 22,the parking lock 30, the loose wheel for the reverse gear stage R, theshift clutch pack SK4/R, the loose wheel for the forward gear stage 4,the loose wheel for the forward gear stage 3, the shift clutch packSK1/3, and the loose wheel for the forward gear stage 1.

FIG. 8 shows a further embodiment of a twin-clutch transmission 10 faccording to the invention.

The twin-clutch transmission 10 f is designed as a 7-gear transmissionand contains two dual uses (for the gear stages 3, 5 and 4, 6) and adrive wheel connected downstream.

The transmission is suitable for an inline arrangement and for afront-transverse arrangement.

Arranged on the first output shaft 16 are: the first output wheel 20,the loose wheel 28′ for the forward gear stage 2, which loose wheel 28′simultaneously serves as a rotational direction reversal wheel andengages with the loose wheel of the reverse gear stage R on the secondoutput shaft 18, the shift clutch pack SK2/6, the loose wheel for theforward gear stage 6, the loose wheel for the forward gear stage 5, theshift clutch pack SK5/7, and the loose wheel for the forward gear stage7.

Arranged on the second output shaft 18 are: the second output wheel 22,the parking lock 30, the loose wheel for the reverse gear stage R, theshift clutch pack SK4/R, the loose wheel for the forward gear stage 4,the loose wheel for the forward gear stage 3, a shift clutch pack SK1/3,and the loose wheel for the forward gear stage 1.

The two output wheels 20, 22 are in engagement with a drive wheel 36which is in turn connected to a differential 26′ which is arranged so asto be axially offset.

In FIG. 9, a first embodiment of an automatic shift transmission isdenoted generally by 10 g.

The automatic shift transmission 10 g corresponds in terms of the wheelset design entirely to the twin-clutch transmission 10 of FIG. 1. Theonly difference is that the drive input shaft arrangement has only asingle drive input shaft 38 to which all of the fixed wheels for theforward gear stages 1-6 are fixed.

In FIG. 10, a further embodiment of a twin-clutch transmission accordingto the invention is denoted generally by 10 h.

The twin-clutch transmission 10 h is realized as a 2-shaft transmissionand has only a single output shaft 40 which is aligned parallel to theinput drive shaft arrangement (composed of the coaxially-arranged driveinput shafts 12, 14).

Arranged on the single output shaft 40, in this sequence proceeding fromthe transmission input, are the following elements: an output wheel 20″which is connected to a differential 26″, a parking lock 30″, a loosewheel for the forward gear stage 2, a shift clutch pack SK2/R, a loosewheel for the reverse gear stage R, a loose wheel for the forward gearstage 6, a shift clutch pack SK4/6, a loose wheel for the forward gearstage 4, a loose wheel for the forward gear stage 5, a shift clutch packSK3/5, a loose wheel for the forward gear stage 3, a shift clutch packSK1, and a loose wheel for the forward gear stage 1.

An additional fixed wheel 44 for the reverse gear stage R is also fixedto the drive input shaft arrangement, more specifically to the driveinput shaft 14. Said fixed wheel 44 is in engagement with a rotationaldirection reversal wheel 28″ which is mounted on an auxiliary shaft 42.The auxiliary shaft 42 is arranged parallel to the drive input shaftarrangement 12, 14 and the individual output shaft 40.

The rotational direction reversal wheel 28″ is in engagement with theloose wheel for the reverse gear stage R on the output shaft 40.

Since no dual use is realized, the transmission ratios are variable. Theforward gear stage 1 and the reverse gear stage R are assigned todifferent partial transmissions.

1. A step variable transmission for a motor vehicle, wherein the stepvariable transmission has a plurality of forward gear stages and atleast one reverse gear stage, having: a drive input shaft arrangement;an output shaft arrangement comprising two output shafts; and aplurality of wheel sets which have fixed wheels and shift wheels,wherein the shift wheels are rotatably mounted on a shaft arrangementand can be rotationally fixedly connected to the associated shaftarrangement by means of respective shift clutches, wherein a certainforward gear stage is assigned to a first one of the output shafts andwherein the reverse gear stage is assigned to a second one of the outputshafts, wherein the reverse gear stage is driven via a rotationdirection reversing wheel which is rotationally fixedly connected to ashift wheel of a wheel set which is assigned to the certain forward gearstage, and wherein a parking lock is assigned to the second outputshaft, and wherein the parking lock is aligned in the axial directionwith the certain forward gear stage of the first output shaft.
 2. Thestep variable transmission as claimed in claim 1, wherein the stepvariable transmission is a twin-clutch transmission, wherein the driveinput shaft arrangement has a first and a second drive input shaft whichare assigned to a first and a second partial transmission respectively,and wherein the first partial transmission is assigned odd forward gearstages and the second partial transmission is assigned even gear stages.3. The step variable transmission as claimed in claim 2, wherein astarting forward gear stage which is used predominantly for starting themotor vehicle in the forward direction, and the reverse gear stage areassigned to different partial transmissions.
 4. The step variabletransmission as claimed in claim 1, wherein the drive input shaftarrangement has a single drive input shaft.
 5. The step variabletransmission as claimed in claim 1, wherein the two output shafts,together with the input drive shaft arrangement, form a 3-shaftarrangement.
 6. The step variable transmission as claimed in claim 1,wherein the certain forward gear stage is the second forward gear stage.7. The step variable transmission as claimed in claim 5, wherein thestep variable transmission is a twin-clutch transmission, wherein thedrive input shaft arrangement has a first and a second drive input shaftwhich are assigned to a first and a second partial transmissionrespectively, and wherein the first partial transmission is assigned oddforward gear stages and the second partial transmission is assigned evengear stages, wherein two forward gear stages of the forward gear stagesof one partial transmission are assigned to different output shafts, andwherein said two forward gear stages share a common fixed wheel on thedrive input shaft arrangement.
 8. The step variable transmission asclaimed in claim 5, wherein the step variable transmission is atwin-clutch transmission, wherein the drive input shaft arrangement hasa first and a second drive input shaft which are assigned to a first anda second partial transmission respectively, and wherein the firstpartial transmission is assigned odd forward gear stages and the secondpartial transmission is assigned even gear stages, wherein two forwardgear stages of the forward gear stages of the two partial transmissionsare in each case assigned to different output shafts, and wherein therespective two forward gear stages share in each case one common fixedwheel on the drive input shaft arrangement.
 9. The step variabletransmission as claimed in claim 5, wherein the first forward gear stageand the second forward gear stage are assigned to the first outputshaft.
 10. The step variable transmission as claimed in claim 1, whereinwheel sets which are assigned to those forward gear stages whichtransmit high torques are arranged at axial ends of the output shaftarrangement.
 11. A step variable transmission for a motor vehicle, thestep variable transmission having a drive input shaft arrangement, anoutput shaft arrangement, and a plurality of wheel sets for establishinga plurality of forward gear stages and at least one reverse gear stage,wherein the output shaft arrangement has two output shafts which,together with the drive input shaft arrangement form a 3-shaftarrangement, wherein a certain forward gear stage is assigned to onedrive output shaft of the output drive shafts and wherein the reversegear stage is assigned to the other drive output shaft, wherein thereverse gear stage is driven via a wheel which is rotationally fixedlyconnected to a loose wheel of a wheel set which is assigned to thecertain forward gear stage, wherein a parking lock is assigned to one ofthe drive output shafts, and wherein the parking lock is aligned in theaxial direction with a certain forward gear stage of the other driveoutput shaft.
 12. The step variable transmission as claimed in claim 11,wherein the certain forward gear stage is the second forward gear stage.13. The step variable transmission as claimed in claim 11, wherein thefirst forward gear stage is assigned to the drive output shaft with theshorter axle spacing.
 14. A step variable transmission for a motorvehicle, wherein the step variable transmission has a drive input shaftarrangement, an output shaft arrangement, and a plurality of wheel setsfor establishing a plurality of forward gear stages and at least onereverse gear stage, wherein the step variable transmission is atwin-clutch transmission, wherein the drive input shaft arrangement hasa first and a second drive input shaft which are assigned to a first anda second partial transmission respectively, and wherein the firstpartial transmission is assigned odd forward gear stages and the secondpartial transmission is assigned even gear stages, wherein the forwardgear stage which is used predominantly for starting the motor vehicle inthe forward direction and the reverse gear stage are assigned todifferent partial transmissions, wherein the output shaft arrangementhas two output shafts which, together with the input drive shaftarrangement, form a 3-shaft arrangement, wherein a certain forward gearstage is assigned to one output shaft of the output shafts and whereinthe reverse gear stage is assigned to the other output shaft, whereinthe reverse gear stage is driven via the certain forward gear stage thatis not the starting forward gear stage, and wherein the reverse gearstage is driven via a wheel which is rotationally fixedly connected to aloose wheel of a wheel set which is assigned to the certain forward gearstage.
 15. The step variable transmission as claimed in claim 14,wherein a parking lock is assigned to one of the output shafts.
 16. Thestep variable transmission as claimed in claim 15, wherein the parkinglock is aligned in the axial direction with the certain forward gearstage.
 17. The step variable transmission as claimed in claim 14,wherein the certain forward gear stage is the second forward gear stage.18. The step variable transmission as claimed in claim 14, wherein thefirst forward gear stage and the second forward gear stage are assignedto one of the two output shafts.
 19. The step variable transmission asclaimed in claim 14, wherein the first forward gear stage is assigned tothe output shaft with the shorter axle spacing.